Lead-acid storage batteries generally require a system of venting to the outside atmosphere to allow gases to escape. While the vents are primarily intended for the molecular hydrogen and oxygen produced by chemical reaction, the battery's electrolyte level will eventually become lower as evaporative water and gas-entrained droplets escape through the vents. Filler caps are added to the battery cover over the individual cells to allow periodic fluid replacement to maintain the desired level and acid concentration. The above functions are often combined by incorporating the venting system into the individual filler caps, and such caps are then commonly termed vent plugs.
Since vent plugs allow communication between the battery interior and the atmosphere, they create a potential for several undesirable occurrences. The flammable vented gases may ignite, and if the flame is permitted to propagate back through the vents to the gases enclosed in the battery, an explosion may destroy the battery and cause damage or injury to surrounding material or persons. This risk is increased in military vehicles, where weapon discharge, explosive and incendiary ordinance, and burning debris on a battlefield increase the potential for battery gas ignition. Military vehicles are also frequently designed to have at least a limited amphibious capability for fording waterways, during which time the battery may be completely submerged. If the vent system allows water to pass into a submerged battery, the acid concentration and electrolyte level could quickly depart from the intended range and degrade battery performance. Consequently, military procurement specifications frequently establish a submersible capability for vent plugs.
In commercial batteries it has been learned that vents should also reduce the likelihood of electrolyte being spewed out of the vents as gas entrained droplets or spray mist. Vent plugs such as described in U.S. Pat. No. 4,052,534 are directed to reducing this occurrence.
An object of this invention is to combine features of flame retardance, submersibility, and anti-spewing into a single vent plug, and to do so in an efficient and effective manner. The described vent plug is intended for military application and therefor to meet military procurement specifications, although the features described may be used in other environments as well. The means by which these objectives are accomplished will be apparent from the following description and drawings.